Positive feed drills are available where the feed is accomplished with a lead screw geared directly to spindle rotation. Other mechanical feed drills are of the differential gear feed type. The majority are right angle drills, while a few are straight, in-line drills. Some such drills are of the peck type which reciprocate rapidly for effective chip control.
Right angle drills were developed primarily for use in small, confined areas which could not accommodate larger straight in-line drills and related tools. Right angle drills offer more power and thrust in smaller, lighter packages than other forms of available drills. Approximately forty percent (40%) of all holes drilled in aerospace structures, where the drill motor is portable and fixtured are drilled with right angle, positive feed drills with differential gear feeds.
Spindle rigidity and concentricity are major problems which have plagued drills, particularly right angle drills. Generally, right angle drill spindles are supported by the thread in the feed gear and the outside diameter fit of the drive gear inside the drill head together with the outside diameter fit of the drill bit inside a drill bushing in the lower end of the tool nose. Such drill spindles, especially in worn drills, can often be visibly shaken when in the assembled state. Such loose drill spindles have been taken for granted in the aerospace industry. Since acceptable tolerances have not been met using such drills, a reaming operation has generally followed the drilling of each hole to meet aircraft quality standards.
One form of drill which has been developed to overcome the quality control problems which have been inherent in drills used in the aerospace industry is known as a "Peck Drill" which produces holes within a few thousands of drill bit diameter without the necessity for reaming. This is an air feed type drill including the motor, gear train, and spindle journaled in bearings within a sleeve. The sleeve fits in a close bore in the drill housing with an air cylinder moving the entire assembly outwardly to feed the bit into the work piece. The spindle is rigidly supported and turns extremely accurately. The sleeve is a quill providing spindle support which is also equidistant from the drill bit tip. Such a drill bit design has been successful for smaller drill sizes, but the thrust limitations have prevented the use of such drills with larger drill bits.
It is an object of this invention to produce mechanical positive feed drills with supported spindles.
It is another object of this invention to provide a new and improved right angle, differential gear feed drill having a supported spindle.
It is another object of the invention to provide a right angle positive feed drill of the character described which has spindle concentricity and rigidity to improve the quality of holes drilled.